In automotive manufacturing, polymeric composites are being used increasingly due to favorable characteristics including being lightweight, highly-conformable or shapeable, strong, and durable. Some composites are further colorable and can be finished to have most any desired texture or finish.
Increased use in automobiles includes, for instance, in instrument and door panels, lamps, air ducts, steering wheels, upholstery, truck beds or other vehicle storage compartments, upholstery, external parts, and even engine components. Regarding engine components, and other under-the-hood (or, UTH) applications, for instance, polymers are configured, and being developed continuously, that can withstand environments being hot and/or chemically-aggressive.
Regarding external parts, such as fenders, polymers are being developed to have online paintability and high heat and chemical resistance over longer periods of time.
Many other potential uses for polymers and, particularly polymeric composites, in automotive applications continue to be developed.
With this trend, finding ways to efficiently and effectively join polymer components is becoming progressively important. Compression molding and post-mold joining techniques—e.g., ultrasonic welding—are being used more commonly, for instance.
In ultrasonic welding, two workpieces are joined, wherein one or both includes a polymeric composite or other polymer. With reference to the figures, and more particularly the first figure, FIG. 1 shows schematically a conventional ultrasonic welding arrangement for joining two workpieces 102, 104 using a welding tool 106.
The tool 106 includes multiple parts, such as an arm 108 and an ultrasonic vibration applicator, or horn 110. The arm 108 is connected to other components, such as a pneumatic or servo actuator (not shown in detail) for controlling vertical displacement of the horn 110.
For welding, components of the tooling 106 are moved to a proximate workpiece 102 of the two workpieces as indicated by arrow 112.
For the ultrasound technique, the workpieces 102, 104 are held together between the horn 110 and an under structure 114, such as an anvil. The pieces 102, 104 are maintained under pressure while ultrasonic vibrations are applied to pieces for the welding.
The vibrations create frictional heat, initially at faying interfaces (i.e., tool-to-workpiece, workpiece-to-workpiece), and then intermocular friction in the composite material, causing the material to melt. When the melting occurs at the interface 116, the workpieces are joined there by molecular bonds (e.g., fusion or covalent bonds) of the molten material.
Sometimes, flawed, or discrepant welds are formed. A discrepant weld, generally, is any weld differing undesirably from a target weld configuration. A common flaw is that a weld is undersized, or otherwise less robust than desired. In one scenario, a discrepant weld can, for instance, not reach the inter-piece interface 116 as needed for joining the workpieces 102, 104 together robustly.
In another scenario, a discrepant weld reaches the inter-part interface 116, but does not bridge the interface 116 as needed for joining the 102, 104 workpieces together robustly.
In the example of FIG. 3, the weld 202 barely reaches the interface 116, and does not connect robustly to the distal workpiece 104.
FIG. 2 shows a subsequent stage 200 of the arrangement wherein the horn 110 provides welding energy 202—e.g., high-frequency (HF) acoustic vibrations—to the workpieces 102, 104. As with the downward force 112 indicated in FIG. 1, a downward force 206 may be applied in connection with the operation of FIG. 2. A molten workpiece material nugget 204 begins to form, in response to the heating adjacent the horn 110, as the vibration is transmitted from the horn into the workpiece 102.
FIG. 3 shows the arrangement, after the erred welding in which the insufficient, or discrepant, weld 300 is formed. There are many factors that can contribute to the weld 300 being insufficient. For instance, workpiece material may be contaminated, one or both of the workpieces may be overly-thick, one or both workpieces may be improperly positioned or not held robustly and so moving (due, e.g., to improper or malfunctioning fixture), improper process variables [e.g., frequency, amplitude, clamping force, or time (e.g., insufficient time)], and/or other conditions may be present.
FIG. 3 shows the weld horn 106 being withdrawn from the newly completed, but insufficient, weld 300.
FIG. 4 shows an example sufficient, desired, weld 400. The weld 400 bridges the inter-piece gap 116 significantly, joining the pieces 102, 104 robustly.
With continued reference to the discrepant weld 300 (FIG. 3), an attempt to simply re-weld the weld 300, using the same tooling and process, would be ineffective at least because sufficient frictional heat will likely not be able to be generated again at the same faying interfaces of the workpiece, as modified, for re-welding. More particularly, the workpiece structure, especially at a surface or perimeter of the previously-welded zone, would have become too constraint to generate sufficient welding heat again.
Attempting to repair a weld 300 by adding additional welds around it is also usually not practical due to limited space, material, time, and energy, as well as for cosmetic considerations.
A surely undesirable alternative is to scrap the workpieces 102, 104 in which the discrepant weld 300 is formed.
Hypothetically, some workpieces improperly joined could be recycled, somehow, but resources would need to be dedicated to determining whether parts can be recycled, recycling the parts that can be, and handling the parts that cannot.
Yet another alternative is conventional mechanical fastening of the workpieces 102, 104 together instead of welding, or after a partial weld has been identified. The workpieces can be screwed together, or connected by nuts and bolts, for instance. These connections have shortcomings including possible lack of durability and mechanical strength. The connection may not be robust due to the fastener connecting to already insufficient joint material. Another shortcoming is that the fastener may need to be threaded in order to maintain connection to the workpiece material over time, and the threading may be insufficient for connecting to some materials, such as metal or polymeric composites.